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Is there an in-flight built-in-test in an airplane?
Is there any in-flight built-in-test in the airplanes separate from the in-flight monitoring?

Of what?  Flight controls?  Avionics?

What are you trying to test?

The thing that separates a BIT/BITE (E=Equipment) from continuous fault monitoring is that the continuous fault monitoring simply responds to exceedances of various paramters or values outside of specified limits in real time as they happen (say where an analog voltage signal of a device drops below a minimum of X or exceeds a maximum of Y), whereas a BIT/BITE test is a specific routine where simulated fault signals are injected into a circuit to see if a fault monitor is doing its job.
BIT or BITE tests of electronic controllers can be categorized into three types:

Start Up BIT: Most common.  A test routine automatically run on power up of the controller.
Initiated BIT: Controllers may have a manually initiated BIT/BITE that can be run any time, but this is usually triggered by a button on the controller itself in the avionics compartment, or through a maintenance access portal in the aircraft maintenance diagnostic system, and usually doesn't have a flight crew initiated facility (but may in some cases).  These are normally intended for troubleshooting.
Continuous BIT: A controller may run an internal self test routine on a continuous cycle while powered up, where a controller has fault detection circuits that can't be allowed to have dormant failures, even for the duration of the flight.

How faults can be injected while the controller is working? Doesnt it degrade its performance?

Not necessarily. The faults are injected by software internally and the microprocessor doing the active fault monitoring can be told it's part of the BITE and to ignore the result.

I do not design this equipment for airplanes, but this is largely the same in industrial equipment. Real time monitoring is an error/warning system with complex responses. Built in test prevents a device becoming operational (or limits operational mode) when it fails. However, I have not had to design anything as elaborate as simulated faults during BIT/POST , generally we rely on OK signals from components and some functional verification.

Yes, in-operation BITs exist.
For example some older analog fuel flow meters have two BITs, one for zero flow and one for nominal flow. The zero flow BIT will move the needle up to a non-zero flow value, while the nominal flow one will move them down to a different low one. This way the instrument can be tested in any condition without risk that the results of the BIT could be misinterpreted.

On modern complex aircraft systems, each LRU (Line Replaceable Unit) will be conducting a number of built in tests on itself continuously as well as checks that only occur when the unit is powered on
For example, the power supply voltages will be monitored for too high/too low voltages, memory devices will be checked for read/write faults, interfaces with other systems will be checked for a frequent stream of data, data buses may perform a loopback test of themselves to check that it is working etc etc.
Any faults may be reported to a centralised maintainance/fault system which will determine whether the pilots need to be informed of the fault.

Is this different from continuous fault monitoring? For example, we know that sensor faults are detected by monitoring redundant sensors and using a majority voting algorithm. If one sensor is different from the others, it will be considered faulty. The same is for redundant outputs of flight control computers. What I mean is that is this monitoring the in-flight Built-In test or it is something separate that is done in addition to this monitoring?

@shooshool Two separate items. BIT will typically be checking the hardware/interfaces of the unit. Voting schemes are to ensure availability of the system even if one sensor/device fails but the the BIT flags reported by a unit may be used by a voting mechanism to ignore the data from one source. For example if one of the airspeed sensors reports an internal fault from a built in test, the computing systems using that sensor will ignore it's data.

A/c controllers can be like that but have to go to greater lengths to mitigate the risks of dormant failure modes. But most of the time a BIT on power up is sufficient. You will also see,especially with controllers related to flight controls that the entire computer channel is split into two completely separate sub-channels, with one actually in control and one "going through the motions" in parallel, like a mime, & another chip watching both to make sure they do the same thing.  Ea sub channel will use a different brand of microprocessor to prevent architecture related defects affecting both.

Absolutely.  Every flight is a built-in in-flight test.  For example, if you perform a 2-g turn and the wings don't fall off, you've demonstrated that the aircraft can sustain 2 g's without structural failure.

How is flying a turn a built-in test?

Maybe answer only applies if the plane eventually enters  the turn on its own when the pilot releases the controls.  In this case the turning tendency (lack of inherent tendency to stay wings-level) would be built in to the design.  This would be a good description of most modern aircraft.

I don't think you are using the usual definition of a built-in-test.


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What is "airside inspection"?
Today, I flew on a commercial airline European flight. Upon arrival, as I was walking from the airplane to the arrivals gate (across tarmac, no jetways), a yellow car labelled "Airside inspection" sped up to the plane with blue lights and sirens wailing.

An officer ran out and blocked people from exiting the plane (some had already gotten out and were allowed to leave). Then, other two people in orange jackets followed him into the plane.
Google searches for airside inspection don't produce a lot of material, but from what I could understand these people are charged with checking that the runways etc. conform to safety standards.
What reason would they have to approach a plane, sirens on, and block the passengers?

What airport was this at?

@TomMcW that pic is of a brussel's airport vehicle from the text on the front door.

@ratchet freak I zoomed in and saw that after I posted the comment But I'm still not sure where the photo came from, if he took it himself or found it somewhere. Looked up the Brussels regulations and the only thing I could think of is if the crew did something improper. Hard telling, any answer would prob be conjecture

@TomMcW the picture is from flickr but it happened indeed at brussels airport and that was the exact vehicle. is the term "airside inspection" common in other airports though? what are they responsible for?

See page 56 (section 3) of ACI Airside Safery Handbook.

It seems they are responsible for everything from fod on the runway to security on the ramp and runway area. That's why I'm thinking they may have neglected to follow procedures.

"Hey buddy, you can't park here! Can't you read the sign?"

@TomMcW I see, thank you. Seems weird to me that they would stop the passengers, and that they would even have such authority on us.

Oh, I'm sure they have authority. Anybody walking on the ramp, from passengers to employees to unauthorized persons, to even wildlife would be under their jurisdiction.

Can you clarify what you mean by "other people in orange jackets followed him in." Into where? The plane, the terminal?

@fooot into the plane. edited.

As the comments have explained, "airside inspection" is tasked with addressing issues "airside," which means pretty much everything inside the airport perimeter, and outside of the terminals.
Just about anything airside will affect the safety of aircraft operating at the airport. For this reason, there are generally many regulations and rules that apply to operations here. Airside inspection involves making sure all of these rules and regulations are followed. This can be anything from addressing security issues to removing FOD (foreign object debris) and ensuring markings and signage are in working order.
Since they are responsible for managing activity on the airport apron, they absolutely have the authority to stop anyone that is in the wrong place at the wrong time. Although there may not have been any apparent issue, there could be regulations or dangers that not everyone is aware of. If the flight crew sends passengers out onto the apron when they shouldn't, this is an issue that the airside employees would want to address.
There are various descriptions available for positions that involved airside inspection, including some of the duties involved.

Maintains safety and security on airport premises; ensures TSR 1542 compliance; patrols,inspects, searches and escorts as necessary; conducts identification checks and permits access only to authorized individuals; provides security training as necessary.
Patrols and inspects airport operational areas for potential hazards; ensures compliance with FAR 139 and other federal and local rules; monitors and controls vehicle traffic on taxiways and runways; patrols all airport facilities, airside and landside.
Monitors and controls vehicular traffic on taxiways and runways and public roadways and parking lots; checks for proper ID on vehicles and personnel entering the Airport Air Operations Areas (AOA).
Ensuring compliance with all safety/security regulations and standards within our activities and ground handling operations.
The management of a safe and efficient airside operation by carrying out Airside Inspection Audits and Flight Turnaround Audits.

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Why are the lights inside commercial airplanes turned off during take off and landing?
Before landing and taking off, I notice the lights inside commercial aircraft are greatly reduced. I don't buy the explanation of power saving in case full thrust is needed as nowaday lights don't need a lot of energy and the crew says we can use the smaller reading lamp to continue reading. I suppose this is something to do with security but I don't understand what.

or a better view for the pax sitting in the window seats

So they can see through the rear-view mirror, of course.

This is for safety reasons.
Take-off and landing are the two most critical phases of flight and thus, every additional step to ensure survivability, be it even just adjusting the light, is taken.
The interior lights or cabin lights are adjusted to match the exterior environment, so that in case of an emergency, especially if the interior lights fail, your eyes are already accustomed to the light setting and you do not require additional valuable seconds for adjustment to a possibly darker or brighter environment. The lights are usually adjusted at dusk, night or dawn to match the exterior environment.1
If the cabin lights do not fail during an emergency, the dimmed light also makes it easier to identify the "EXIT" signs which illuminate and make the guidance lighting on the floor easier to follow. The bright emergency lighting is more prominent to identify when the cabin light is dimmed, saving valuable seconds as the aircraft is evacuated.
This also ties in with having to raise the blinds on the windows. The blinds need to be raised during take-off and landing irrespective of the outside light situation, however, with a darker cabin, any outside light source, especially from fires or other hazards is easier to identify by the crew, making the decision process of whether one side could be inappropriate to use for evacuation faster, e.g. fire on port side --> no evacuation on that side.
The blinds are therefore raised to allow a better view for cabin crew of the outside area and external aircraft parts, such as engines, wings, etc.
See also this related question: Why open up the window shades before takeoff and landing?

Note that in addition to SentryRaven's informative answer, some airports, such as Kabul, require turning off all lights (and landing at a steeper angle) for security reasons. See this answer from Travel.SE for a first-person account of landing in Kabul.

Noticing the floor lighting is important, but having your eyes already adjusted to the outside is more important. If you just follow everyone else, you should find the exit just fine. Once you're outside, people will be spreading out and having your eyes already adjusted to that environment can save lives.

Do you have a source for all this? The explanations I read before (including on travel.SE) are slightly different.

What in my answer is different from the reply on Travel.SE @Relaxed?

@SentryRaven You emphasize the darkness of the cabin and the role of the crew, as opposed to preparing the passengers to evacuate (including, when applicable, by adjusting to bright sunlight).

You are correct and I have rephrased part of my answer to reflect other explanations I have found online. I linked one of the sources that are directly from an airline, which gives it a bit of credibility. I have not found other quotable sources though. @Relaxed

@SentryRaven Thanks for the research!

@dotancohen: Granted, I doubt many of us are planning to fly into Kabul anytime soon.  Not because of the flight, but because of the destination.

My flight instructor told me that also, when taxiing at night (that is, before taking off or after landing), lights should be kept at a minimum as a courtesy to other pilots. A bright line of full lit cabin windows could distract or mask other dimmer lights like the taxiways blue ones.

This is generally more of a concern with bright external lights (like strobes), but it's an interesting point...

You are right.
The 'power saving' theory is nonsense. Most of the time, except at 'hot and high' airfields, aircraft take off using much less than maximum engine thrust (known as de-rated or 'FLEX' thrust setting), so turning off the lights to reduce the generator load doesn't make any sense. It is also worth noting that cabin crew require the lights to be dimmed during landing as well, not just take off, and that would have no 'power saving' benefit whatsoever. The A/C packs may be turned off during take off because they use bleed air from the engines, which does have an effect on thrust output. This would only really be necessary with a high take off weight or short runway.

Although your answer provides usefull information it does not answer the question (Why are the lights turned off).

Cabin lighting has no impact whatsoever on takeoff power.  None.  Reducing cabin lighting does not increase power available for takeoff.
Cabin lighting is dimmed for takeoff to help ensure that emergency lighting is most visible.  Reduction of cabin lighting aids in dark adaption.
I have never seen an aircraft performance chart or program that accounts for cabin lighting on or off to determine available power for takeoff...because with respect to available takeoff power, cabin lighting is irrelevant.
And yes, we do dim lighting during arrivals and departures in Afghanistan.  It still has nothing to do with takeoff power.

The "line" about needing full power for takeoffs and landings is true. I was taking courses for an Airframe & Powerplant certification for airplane mechanics. According to professors at what used to be the Northrop Rice School of Aviation Technology in Los Angeles, California, all power in an airliner is diverted to the engines for maximum thrust on takeoff. That means the lights are turned off or dimmed and even the air conditioning is turned off until after takeoff. As we all know, the airplanes are getting bigger and bigger. However, the length of the airport runways has not changed much at most of the airports. That means that the pilots of these jumbo jets have to get up to their airplane's noted speed for takeoff faster (before they run out of runway). So all "redundant" systems on an aircraft are shut down so that power can be used to get that airplane off the ground safely in the distance they have to get lift. Flying is all about the power to weight ratio on any aircraft. But the jumbo jets require a much higher speed to be able to take off.

Martin, no offence, but without some serious sources this answer just sounds like nonsense. As below, nobody turns off these systems during the day and I can't believe for a minute the load makes this kind of critical difference to the output of the engines.

So why are the seat back entertainment systems left on?

@Simon: Apparently, they often aren't.

99.9% of takeoffs are done with less than 80% power output... because planes don't need full thrust to take off in most cases.

Large aircraft have tables of adjustments to runway length and power setting, they do not dump full power at every takeoff this is hard on the engines and the added noise angers the people who foolishly purchase houses next to the airport. beside that after V1 speed they can [and must] continue takeoff and climb on one engine. All quite calculated based on air density, takeoff mass, runway length, and climb gradient over obstacles.

You better start believing in the explanation of power saving.
I couldn't find the reference, but there was an accident over 5 years ago in which a plane was taking off with many non-essential loads at or near maximum: air conditioning, galleys heating food, cabin lights.
One generator failed, and the system supposed to shed non-essential loads also failed. The remaining generator wasn't designed to stand so much load, so it failed too. Loss of power to essential loads.
Since then, airliners take off almost simulating an electrical emergency. Reading lamps are a reasonable compromise because very few people actualy use them.

This argument would be much more compelling if you could include some links or directions to the source material.

I suggest that this is nonsense because the interior lights are only dimmed at night, not during the day (when they are still at full power!).

I would also disagree with this answer, on the grounds that it is not the cockpit crew who controls cabin lighting (on all planes)

No airplane takes off "almost simulating an electrical emergency".  You also lump air-conditioning in as an electrical load, wheras it is actually a pneumatic load and while that will be a bigger impact on performance than the generators, it is dwarfed by anti ice activation, which is run during takeoff into icing.

Do you have a link to the flight, or AAR?

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What would be the drawbacks of using a rotating engine as thrust reverser on airliners?
What are the drawbacks for having engines mounted on an aircraft such that their direction can be hydraulically controlled for best performance and efficiency? The idea would be to turn the engine 180 degrees at landing so it can operate as a thrust reverser, even on jumbos like the Airbus A380 and the Boeing 747.  That would be some serious thrust reversing power.

Yes, in principle. But how do you manage what happens during transition? Either you rotate horizontally and create massive side forces, or you rotate vertically and hoover all dirt from the runway during transition.

It would be serious power:  virtually enough power to sustain flight backwards, which is way more power than is needed.  That's called over-engineering.   The current thrust reversers are reliable, small, light, responsive, and don't do more than is needed.

Or the whole aircraft, like the ice skaters in a show.

Oh boy... angular momentum problems, FOD ingestion, excessive complexity, lack of space, extra weight, slow response time... not to mention that all of the (presently) fixed external connections to the engine (fuel, electricity, controls, etc) would now need to be unfixed and moving - the maintenance headache for this alone is cringeworthy.  It's a terrible idea in just about every respect.

In addition to all the other issues people are naming, I'm wondering about the risk of compressor stall. Would the engines be able to maintain working pressure ratios when turned around backwards? Of course, regular thrust reversers can produce compresser stalls as well.

Aside from all the technical details in the answer and comments, you can dump this idea because of just one issue: however you try to rotate the engine, when it is half-rotated it is effectively flying in a 140 knot cross wind(and that's a minimum number - the aircraft speed might be higher.) Compare that with the maximum allowable crosswind for a 737-800 takeoff on a wet runway, which is just 27 knots - and ignoring that limit is quite likely to perform a "very rapid disassembly operation" on the engines!

Mental picture: Do you really want to have the full thrust of all engines pulling the plane's wings out, driving them into their roots, or pulling the wings towards the ground during the forward-backwards engine swing, especially at landing?

your title asks about airliners, but the body mentions aircraft. what exactly are you interested in?

Bigger wheel brakes are cheaper, safer and lighter:)

@Koyovis I would love to see standard landing practice like that.

I wouldn't worry to much about the mass of the engine. That's actually not the biggest problem. Instead, I'd be scared far more by the angular momentum. That turbine has a large moment of inertia and also a higher angular velocity.To flip it, you have to reverse the angular velocity. It's essentially flipping a gyroscope, but this is a gyroscope weighing several tons.

Exactly what I was thinking. Take the front tire off a bike and hold the axle in your hands (might need trick extenders to do this properly). Rotate it upside down. Pretty simple. Now have someone spin it and do the same (at most 100 RPM). You'll notice it's not as easy. I can't imagine the momentum on a jet turbine rotating at 10,000 RPM

If you try to flip a gyroscope in mid air, the gyroscope will try to flip you.  This is how spaceships rotate.

And yet this is exactly what the V-22 does.

@Koyovis Yeah, 90-deg rotation in 12 seconds for a powerplant a tenth the size of a 747's RB-211s.  You'd be off the runway before they got turned around for reverse thrust and in the cow pasture if you ever needed to go around.

Solvable with good design: 1) side-thruster, similar to a thrust reverser, to counter it.  2) Pairs of engines counter-rotate, A400M style, canceling each other, yes I'm aware only the props counter-rotate, not the engine core, but hold that thought: 3) parts of each engine counter-rotate against each other, canceling it within the engine; e.g. opposite turning spools or fan or prop geared to spin opposite of spools (half of A400 engines).

Well, counter rotating or not, the amount of torque required to rotate a running turbine is excessive, and the force you have to supply from whatever fix point (even if this is balanced by another rotation) means the structure you build around this fix point has to be extremely hardy. The bearings and the axle will likely make the "rotator" bigger than the turbine house...

@Harper A shipload of engineering bolted onto a bad design does not make it a good design.

First drawback is going to be speed of response. The engine is big and heavy, so you aren't going to be able to spin the whole thing around in a tenth of a second. Realistically, it's going to be a few seconds to spin it around. A traditional thrust reverser moves only a very small mass (little flaps, etc), so can react much quicker.
Second drawback will be weight. Any type of rotation system is going to very heavy. You'll be flying thousands of pounds around that are only used for a few seconds during the entire flight.
Third is going to be reliability / safety. What would happen if your engine spun around when you did not want it to?  E.g. what happens if the rotation system fails and you spin one engine around during takeoff?  That would obviously be bad. You need to design the system such that the probability of an accidental reversal is essentially zero.  That's possible, but it is going to drive a lot of cost into the system.

There will be only drawbacks, and some small practical problems such as how does the air stream into the engine when the inlet is facing backwards and we've just touched down at 150 knots.
Current thrust reversers achieve about 50-60% of reverse thrust, and the system weighs between 15 and 20% of the engine dry weight. They are very beneficial on wet and icy runways, but have to be toted around the world for the few times they make a difference.
In fact there has been a NASA report titled Why Do Airlines Want and Use Thrust Reversers? stating all above drawbacks, mentioning that savings on brakes is less than cost of the thrust reversers, and exploring what alternatives the airlines would like. The main interest was the use of variable pitch fans, so that the fan can generate the reverse thrust like propellers can. Weighs less than a classic thrust reverser too.

Update
A 1972 article from Flight Magazine on the variable pitch ducted fan development. It actually worked: it could produce reverse thrust from adjusting the fan blade pitch. A proven working design, always a better option!

It seems like a variable-pitch fan seems like it would have a lot of different problems, mostly related to the effect on airflow to downstream components, such as the low pressure compressor. Air flow through the core has to remain unimpeded for the core to keep running. Sounds like a compressor surge waiting to happen. Also, wouldn't the blades strike the adjacent blades while they were rotating to negative pitch? Or else, the width of the blades would have to be reduced to prevent this.

Yes indeed. An old textbook of mine mentions a solution designed by Dowty-Rotol, but that evidently did not make it into the mainstream.

@reirab And yet the Progress D-27 has no trouble functioning.  Also, engine proper is nothing more and nothing less than a modern peaking unit or destroyer engine (the aeroderivative kind, not the huge cast-iron base kind) it does not need to be axial to the fan, or its intake could be ducted from elsewhere (727/L1011).

The planes would lose the capacity to suddenly abort the landing.
If something unexpected happens just before or even just after touchdown, the pilots have the option to give up, set thrust to maximum, and "take off again". Then try to land again, maybe somewhere else depending on the issue.
It's an important safety feature.
If the thrust reversers are much slower to turn off, requiring flipping the engines back to position, that capacity is greatly diminished. So, less safe, unless you can make it as fast as current thrust reversers.

Maybe someone who flies an airliner can correct me, but I was under the impression that deploying the thrust reversers constituted committing to the landing anyway in most (or all?) airliners. See for example Why are you required to commit to a full-stop landing if reverse thrust is selected?

Some aircraft (Vertical Take-Off and Landing craft) can do something relatively similar with variable thrust direction. In the list of VTOL aircraft it should be noted that rotation generally either occurs because of ducting (i.e. the Harrier Jump Jet) or rotation of the wing surfaces (i.e. a Bell V-22 Osprey)
Looking at the wing of a A380, none of these are really feasible (with the 747 being very similar)

The safest way to rotate the engine would be to pitch it backwards so it still provides lift before reversal (yawing it would create all sorts of chaos in the airframe and control). So you would have to rotate the engine on the pylon. That means a larger pylon and some way to move the engine so the housing can complete the reverse pitch. But there's not enough room to do that. You'd have to somehow extend the engine in front of the wing first and then rotate it around its axis. That's a lot of work for a small amount of benefit.

Can you elaborate on how yawing would cause problems?  Is it that the wing isn't engineered to take compressive loads along its length, or something else?  I would assume that the yawing would be done in opposite directions on opposite wings, so at least you wouldn't have a net thrust off-axis.

@MichaelSeifert I'm no expert at airframes, but even if you rotated all the engines to counterbalance, you're adding some compression stress to the frame by doing a yaw instead of a pitch. If one is even the least bit off, now you risk losing control at the critical moments before landing.

4-engine craft, rotate the engines so the fans point away from the fuselage - you end up with hot exhaust pointing at the fuselage and the outer engine trying to melt the inner one. Rotate so the fans point toward the fuselage, now you're limited to just the inner engine trying to melt the outer one. (Oh, and you've got one engine exhausting directly into the intake of the other, which ever way they rotate.)

@qqjkztd Thrust reversers normally aren't deployed while airborne, anyway. They're generally deployed after touchdown.

Current thrust reversers allow aircraft to land in the same or less distance that they can also take off, without needing huge landing gear and brakes. Shortening the landing distance isn't going to help with shorter airfields, unless the takeoff distance is also shortened. Otherwise, the plane is going to be at that smaller airport until it is disassembled and trucked away.
Here is a video of a C17 that was headed to MacDill AFB, but accidentally landed at a small uncontrolled regional airport. Bit of a problem, as the airstrip was 3400 feet long, and the C17 has a 3500 foot takeoff run. Offload of cargo, a minimum of fuel, and a very gutsy pilot gets it back off the ground.
So a more powerful thrust reverser would add cost, weight, complexity, and more points of failure, without achieving any real benefit. One could shorten takeoff distance with a STOL design, but that would also shorten the landing distance by virtue of a lower minimum airspeed.
Finally, consider the one aircraft today that does have rotating engines: the V22 Osprey. It had a very difficult development cycle stretching over 20 years. When Bell designed a smaller version for the US Army, the V280 Valor, they opted not to rotate the engines, but just the rotor heads, with a clever bevel gear arrangement driven by fuselage mounted turbines.

“The one aircraft today that has rotating engines”?

There is one class of aircraft that does pretty much exactly this thing, the modern Zepplin NT air ships.
They have engines on out riggers that can rotate to provide thrust forward, backwards, up or down (In addition to a fixed pusher prop).
In addition they have a prop at the rear mounted on a rotating collar that can be pointed at right angles to the hull in any direction to provide a means to push the stern around (And also control pitch).

Image source
Not by all accounts the easiest things to pilot.

The title does ask about airliners, though.... Rotating the fans on a very slow airship is quite different from rotating a monstrous high-bypass turbofan on an airliner at airliner landing speeds.

Not at all sure, so I'll ask: Do the props continue rotating while the engines change direction or do they stop them? After all, they're not needed to keep the ship in the air, all the lift is provided by the helium.

The ones I have seen flying do not stop the props, but I suspect the engine is actually fixed and a bevel gear arrangement is used to drive the prop.

@reirab didn't the Hindenburg-era zeppelins count as "airliners"? ;)

"Serious" thrust reversing power could result in pitch up at slow speeds. Thrust reverse is limited to limit the amount of positive pitch movment that could put an aircraft onto its tail (especially when stationary and applying brakes).


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By what parameters can a pilot be evaluated after a flight
As soon as the plane has landed, the "flight information department" receives flight parameters, including "overload" (as an example), what other parameters may indicate the correct operation of the pilot?

Are you talking about a large commercial carrier like United or SAS,or a small charter company, or a trainee working on his PPL, or something else entirely? The more detail you [edit] into your question, the more applicable the answers can be.

You could measure his heart rate, breathing rate, blood oxygen levels- an abnormality in any of those would probably indicate the pilot was not in proper working order.

If you are referring to commercial airline operators, then you most likely meant a Flight Operations or a Flight Safety department receiving this information. Most airplanes do not automatically send all of the information to the headquarters but rather store it in an onboard storage device, then this information is downloaded from the aircraft during scheduled maintenance (every 3-4 days). However, newer aircraft can and will transmit any abnormalities (e.g., high oil pressure, engine fire) directly to the company in real time.
As far as what parameters are used, there are too many to list. Most important values that the airlines look for include the rate of descent, approach speed (ensuring that it is appropriate for the phase of flight), flight path and aircraft altitude over certain waypoints, and the use of flaps/landing gear. All of this is covered under the Flight Operational Quality Assurance (FOQA) program.
Fun fact: Airline management have only access to de-identified information, meaning that the data does not show the date of flight, pilots' names, and any other information which could identify who flew a particular aircraft on a particular flight. The purpose of FOQA is to analyze the operation as a whole rather than look into each individual pilot. The latter is completed during pilot proficiency checks which are conducted regularly.

The de-identification referenced is the case in the USA, but is not necessarily the case elsewhere. Carriers in the Middle East such as Emirates and many (possibly all) Chinese carriers, for example, most certainly do use FOQA data for punitive purposes.

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Why are there two different throttle designs for the 757 and 767?
There is this one, which seems to be the older version. Notice there is a big gap between each lever, except at the top.

And this one. Notice there is almost no gap between each lever, making it appear "bulkier."

What do you see as being different?  They both look like dark metal on the outside and light gray concave on the inside.

Any difference between the photos is probably due to lighting and color cast.

@Jim I'm pretty sure OP refers to the levers themselves, not the "handles". The ones on the bottom are bulkier.

@DeepSpace Correct. The levers are the same, but the handles on the second ones are much “bulkier,” as you described.

There is even a third design used on the 767-400ER, based on the 777 thrust levers. See this Boeing magazine.

I think it depends on what is behind the throttle levers, but that's just a garden variety wild-a** guess.

@757toga So, is the difference in engine control based on the manufacturer? For instance, let's say RR uses cables, but GE uses wires.


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Why were these crash location not located via ELT?
On Jan 14th 2019, at 9.10 Indonesia time, the CVR of the crashed Lion Air JT-610 has been found. Another vital device was found earlier.
There are three modern airplanes crashed in to water in Indonesia:

Adam Air, registration PK-KKW, Boeing 737-400, flight KI514, on 1-January-2007, crashed into Majene Sea due to the failure with the Internal Reference System (IRS), rested in 2,000m below the sea surface.
Air Asia, registration PK-AXC, Airbus A320-216, flight QZ8501, crashed on 28-December-2015, into Karimunjawa Sea, due to the failure with the rudder-travel-limiter.
Lion Air, registration PK-LQP, Boeing 737 Max-8, flight JT-610, crashed on 28-November-2018, into Java Sea. The crash cause is still under investigation.

Those three crash locations were found not by the electronic instrument system, but by fishermen.
Then my question is: why did the modern airplane has not been located via its ELT?

Ordinary electromagnetic waves don't work under water (extra low frequencies work to some extend, and not very deep). That 's why submarines use (ultra)sonic transmissions to communicate between themselves (like whales do). Ultrasonic "pingers" are added to CVR and FDR, to locate them underwater.

How does an ELT work? What does trigger it?

@mins: And the frequencies that do go through water need antennae many kilometres in size in order to produce useful amounts of them.  Not exactly something you can fit into an aircraft's ELT...

@Sean, agreed (more on this). However this is the electric length taking into account the velocity factor which counts. By selecting the proper material and using clever current-to-wave conversion techniques we can sometimes make miracles. An alternative to the plain old Gertrude.

ELT's are not required to be built to the same standards as the CVR and FDR. That means they are much more likely to be destroyed in a severe crash. Also, ELT's (the old style 121.5 and 243 mhz and the new 406 mhz) are not designed to function under water or mud.

And they really cannot be built to the same standard as the recorders, because they need antennas and there is no practical way to make an antenna that will not tear off at hundred G deceleration. It usually tears off beyond some 20–30 G.

Good point, @JanHudec. My first thought was "external antenna" and then the "D-Oh!" hit me with a great big "THUD!" LOL!

Salt water is conductive. The e-field part of the radio wave is effectively short-circuited in salt water. Radio waves attenuate very quickly when travelling through it.
This is out of date, but may lead you to more current information.
My notes from when I was involved with ELTs on commercial jet transports.
https://eltrequirements.homestead.com/
https://eltrequirements.homestead.com/files/fars.doc


text:
What kind of damage would low-level supersonic flight inflict?
I was watching a video about "The Big Stick" aka Project Pluto, a nuclear powered SLAM. In the video (I couldn't find the exact video) it said that after deploying its weapon payload a SLAM could fly over its target country as a "vengeance weapon", causing destruction with it's sonic boom for weeks and an altitude of just a few hundred feet.
What kind of damage would a mach 3 flyby at 200 feet cause?
I'm interested in both building damage and possible human injury.

Flying supersonic "for weeks" is far, far off into the realm of science fantasy. The linked article states that in testing the prototype engine never ran for more than 5 minutes before the project was cancelled, and nuclear powered aircraft have never proven to be viable.  Leaving aside all of that, asking about low altitude sonic booms & the damage they cause is a perfectly fair question, so the upvote is based on that. But please let's set aside visions of "nuclear-powered aircraft flying for weeks..."

@RalphJ the main reason for the short test duration was the inability to provide the Mach 3 airflow through the reactor for longer than that.

The Mythbusters proved that the sonic boom itself would do essentially no damage to glass. To be fair, though, the boom would become a psychological weapon against people after a while. Also, they were testing at Mach 1.0 give or take a bit, not Mach 3.

"Causing destruction with its sonic boom for weeks"  is what originally limited the Concorde to a few overseas routes.  These issues will hopefully be resolved with more modern designs and materials.

The video is highly inaccurate in that area.
The actual damage the missile would have caused would have been largely radiological, from ejected radioactive material in its exhaust plume.
While windows and weak structures may receive damage from extremely low flying Mach 3 bodies, this would probably be limited to say some broken glass.
The plan was also never really considered. What was considered is having the weapon, now without its warheads, fly to a final target area and do a high speed dive into the ground, the kinetic energy alone combined with the spread of radioactive material from the rupturing nuclear reactor causing the damage there.
Mind that the damage (both physical and radiological) of the weapon flying overhead isn't clear. Different sources list different predictions.
Some way the damage would be minor, others that it would be severe.
But rest assured, the noise would shatter eardrums, the supersonic shockwave flatten crops and lightly constructed buildings, and the radioactive exhaust plume wouldn't have been healthy either.
I've always found this to be an excellent article on the project and the people surrounding it.
Edit: a very interesting article by the designer of the reactor about the problems inherent in the reactor design, and how he thought about the radiation hazard for people on the ground working with the missile:
Merkle public paper

While the extra info is interesting, It would be good to focus more on the title question and the question in bold in the post. The stuff about radiation doesn't answer this and wasn't asked about.

Unrelated to the nuclear ramjet aspect, a close high-Mach flyby has many of the same effects as an explosion.  The shock wave has a pressure profile very similar to the "N wave" of an explosion -- positive overpressure followed immediately by a vacuum underpressure -- and depending on the shape of the supersonic object, there may be multiple overpressure waves.
Historically, sonic booms were fairly common when I was a child, if you lived close to an Air Force Base; I grew up about 150 km from Fairchild AFB (Spokane, Washington) and used to hear the booms once or twice a week.  This was in the 1960s, before the ban on non-emergency supersonic flight over populated areas.
Even with an aircraft flying at high altitude (FL200, at a guess), these booms could and would rattle windows; they were loud enough to startle people, sometimes leading to kitchen injuries (dropping hot items, for instance) or falls.  Given that the intensity of the pressure wave from a linear source like this obeys an inverse law, such a boom (from aircraft that were only low supersonic, probably Mach 1.1 to 1.2) from a hundred times closer would be a hundred times stronger -- and go from rattling windows to breaking them, flying glass injuries, many falls (people knocked off their feet by the pressure, never mind off ladders), and so on.
Look at the damage at Chelyabinsk from their bolide explosion a few years ago -- while that object was, well, rock-shaped, at high altitude and much higher speed, that's the kind of damage you might expect with a fairly close supersonic flyby of a streamlined aircraft or missile.

I don't think a shockwave from supersonic object follows inverse square law, just inverse law. The shockwave is a cone, but it is also constantly fed energy, so energy from  any point on the flightpath spreads as a ring on the cone and that only grows linearly with radius, not quadraticly, so the power density only drops with distance, not square of distance.

@JanHudec You're probably correct -- like the light spread from a fluorescent tool of "infinite" length rather than one that looks like a point from a couple km away.


text:
Is it possible to fly a Cessna 172 vertically?
My question has two dimensions:
Disclaimer: Hypothetical question, I am a humble private pilot!

How fast you need to be and how fast you need to turn up so that you do not burn out all your kinetic energy in the lower arc of the climb and at the top you have enough authority to bank and dive back, not simply come to total stop and crash down like a rock.
Is Cessna capable of handling the kind of G's and maneuverability? Can it turn up into as sharp a rotation as required!

"Is Cessna capable of handling the kind of G's", I thought this was the basis for the first question. Do you have really two questions? I think this answer does deal with the zoom climb, in general (only a bit of the answer).

Not sure how vertical flight can be achieved by banking and turning...

@Koyovis, I mean at the end of  climbing you just don't stall or crash and fall like a rock. You still can bank left and descend!

I think what you are asking is if the Cessna 172 can perform a Hammerhead. Yes, it is possible, although the vertical portion will be short, and I believe a properly executed hammerhead is less than 2G including the pull up.

Here’s a C152 performing aerobatics. There are a few videos on YouTube of 172 aerobatics, but they are all cockpit views, so a little hard to tell exactly what they’re doing

@RonBeyer - that sounds like it ought to be an answer (I'd upvote - it provides the requested information, and helps to find more resources by giving terminology).

Might be a good idea to stay humble.  Any type of acrobatics may not be recommended if the aircraft has
a gravity only fuel feed.  Keep in mind if (for example you attempt a loop) and you only make 1/4 of the way through (and are nose up and have lost all forward airspeed), 5 things can happen. Fall straight down tailfirst (will not last long as this is most unstable and the nose wants to be down), tip left, tip right, nose drops back to horizon, nose falls INVERTED to horizon.  The last one I would not want to be in.
Tipping left or right can be helped with rudder and is known as the "stall turn" or Hammerhead.  Nose dropping to horizon would be similar to a stall recovery.
There are aircraft much more suited to do this and qualified people who would be happy to take you up and show how it is done. You may wish to speak with them.

Well the C-172 is certified as both a normal and utility category airplane with a maximum load factor of +3.8g/-1.52g when loaded within the normal category envelope and +4.4g/-1.76g in the utility category envelope.  It is approved for erect spins in the utility category.
As for ‘hard maneuvers’, fly the airplane by the approved maneuvers listed in section 2 of the AFM after receiving qualified instruction on them in the airplane.  Neither I or anyone else here who are pilots and flight instructors can help you with anything else.


text:
How miraculous was the miracle on the Hudson?
The "miracle on the Hudson" was extremely unusual - dual engine failures and successful off-field landings in commercial A320-size aircraft are very rare. The event has been dramatized and the crew (and captain "Sully" in particular) have been widely praised as heroes.
The crew certainly did an excellent job ensuring that all those aboard lived to tell the tale. But was it really exceptional? Aren't all commercial pilots trained to handle emergencies? I don't want to belittle the fantastic job the crew did, but I wonder whether they did something no other crew could do or whether this is something most crew would be able to handle if called upon.
Here is a more precise question:

If a random commercial airline crew were placed in the same situation as the crew of US Airways Flight 1549 on 15 January 2009, how likely is it that they would achieve an outcome with no fatalities?

I understand that to a certain extent this is a matter of opinion, but I hope people can provide some objective comments about what situations crews are trained for and whether there are other comparable examples with similar or differing outcomes.

How 'random' are we talking? A random U.S. mainline crew? A random U.S. crew? A random crew from anywhere in the world? The results will not necessarily be the same. As far as comparable examples, there are very few (dual engine failure immediately after takeoff is extremely rare in airliners.) Likely not enough to produce any kind of numbers with meaningful statistical significance.

In the NTSB report, they note that they had several flight crews fly this scenario in a simulator. Of those that ditched the aircraft, rather than trying to turn back to the airport, all did so successfully.

If im not mistaken, they experimented with a number of crews in a simulator, and gave them differing instructions ("attempt to return to a rrunway", "Attempt to ditch on the hudson" etc).

Possible duplicate of How, exactly, did US1549 land on the Hudson?

It is miraculous because it was a water landing, which is much different than a ground landing. Water landings are insanely hard to do without destruction of the aircraft. When an aircraft hits water at a high speed the water will push into any little crevice or joint in a way that earth won't and will rip the aircraft apart. This is why when a high-speed water craft crashes it usually gets obliterated.

@Chris: I would also expect that if water manages to pull a piece of the aircraft apart even slightly, localized drag will rapidly increase by orders of magnitude.  A simulator may be able to judge how accurately a pilot can match a desired impact angle and airspeed, but I'm curious how much is known about how angle and airspeed affect survival outcomes.

@JasonC The question you link to focuses on the role of the autopilot in the ditching. My question is about the role of the crew.

@supercat: IIRC, Captain Sullenberger mentioned in an interview that most simulators cannot simulate ditchings precisely because of the lack of such data, and also probably more simply, because nobody programmed them to. Simulators typically have fairly precise and accurate aerodynamical models as well as models for fuselage, airframe, engine, and control surface behavior and stresses, onboard systems, etc. They also have models for ground behavior, rolling and braking resistance on different surfaces etc. Yet, they simply don't have hydrodynamical models of the fuselage acting as a boat hull.

One of the key decisions taken by Sully, was switching to APU power as soon as the engines lost power. That contributed a lot towards safe ditching of the aircraft.

@JörgWMittag: I would expect part of the difficulty is that when testing models in a wind tunnel, one can use the same model for many tests, but tests of the hydrodynamic behavior are almost always going to be destructive.  Still, it would seem helpful to know what angle of attack would yield the best likelihood of having things hold together.

I asked the same question on Skeptics.SE in 2011, and got some interesting answers.

There was Ethiopian Airlines Flight 961 that ditched in the Indian Ocean in 1996 during a hijacking. Out of 175 souls on board 50 survived, but it was said that most died due to drowning from improperly inflating their life vests while under water, and not as a result of pilot error. This was noted as quite possibly the most successful ditching in Air Travel history and was captured on video by tourists off shore, at the time. This would have been a far more stressful situation.

The reason I say this (while somewhat subjective) is because this pilot had to endure hours and hours of duress from the hijackers while maintaining enough calm to successfully ditch a Boeing 767 in open waters (much more choppy than a river), which is a lot more difficult to do without breaking up the aircraft upon impact. The pilot's landing was actually a huge lesson in aviation ditching, because he carefully attempted to land parallel with the waves instead of against the waves in an effort to smooth the landing. All this while fighting with the hijackers. But ditchings are never easy.

This would be an extremely difficult question to answer without being opinionated, but I'll give a try. As part of the investigation, the NTSB, along with other agencies carried out a number of tests on simulator, where pilots were tasked with either landing or ditching the aircraft.
There were three different scenarios contemplated:

Normal landings on runway 4 at LGA, starting from an altitude of 1,000 or 1,500 feet on approach;

Attempted landings at LGA or TEB after the bird strike, starting both from zero groundspeed on takeoff from runway 4 at LGA and from a preprogrammed point shortly before the bird strike and loss of engine thrust, and;

Ditching on the Hudson River starting from 1,500 feet above the river at an airspeed of 200 kts.

In the first case, all the landings were successful, which is not surprising. However, in the second case, landing was successful in (slightly) more than half the cases, but only where the response from the pilot was immediate (i.e. there was no delay between loss of thrust and decision to return to airport).

Regarding the second flight scenario, 20 runs were performed in the engineering simulator... Five of the 20 runs were discarded because of poor data or simulator malfunctions. ... In eight of the 15 runs (53 percent), the pilot successfully landed after making an immediate turn to an airport after the loss of engine thrust.

In the one case where a (35 sec) delay was included, the landing was not successful.

One run was made to return to an airport (runway 13 at LGA) after a 35-second delay, and the landing was not successful.

It has to be noted that in all these cases, the pilots were already briefed about the manoeuvre they were about to perform.
The third series of tests were conducted to see whether the pilots were able to achieve the target flight path angle of -0.5$^{\circ}$. Only one Airbus test pilot was able to come near that value. From the report:

Regarding the third flight scenario, a total of 14 runs were performed in the engineering simulator in which pilots attempted to touch down on the water within a target flightpath angle of -0.5°, consistent with the structural ditching certification criteria. Two of the 14 runs were discarded because of poor data.
In 11 of the 12 runs, the touchdown flightpath angle ranged between -1.5° and -3.6° (the touchdown flightpath angle achieved on the accident flight was -3.4°). In 1 of these 12 runs, a -0.2° touchdown flightpath angle was achieved by an Airbus test pilot ...

From these simulations, it appears that the flight crew took the correct decision to ditch in the river. Also, we have to take into account that taking decisions in real world under extreme stress is quite different from taking them in a simulator. The report notes that,

The one simulator flight that took into account real-world considerations (a return to LGA runway 13 was attempted after a 35-second delay) was not successful. Therefore, the NTSB concludes that the captain’s decision to ditch on the Hudson River rather than attempting to land at an airport provided the highest probability that the accident would be survivable.

Another thing to note is that there was no simulator training to the pilots, either as part of the airline or manufacturer program. In fact, the dual engine failure scenarios were presented only at high altitudes.

Ditching scenarios were not included in either the US Airways or Airbus simulator training curriculum.

A similar incident happened in case of the Scandinavian Airlines Flight 751, where the pilots successfully landed the aircraft without any fatalities.
One also has to consider the other issues in ditching in water (like the associated visual illusions). From these, we can form the opinion that a sizeable minority of airline crews would have ditched the aircraft successfully on the river after bird strike so as to enable rescue. As for zero fatalities, it would be near impossible to say that with any certainty, as there are too many factors in play here.

Is "not successful" a jargon term, does it imply how unsuccessful the attempt was? Or does it cover anything from "didn't get a round of applause from the passengers" through to "less than 50% of the aircraft came to a halt on the runway", or "didn't reach the runway"?

@SteveJessop -- "not successful" = "didn't make the runway" in this case -- you generally don't worry about being hot and high on final if you're in a glider, and if you are -- a forward slip fixes that in a jiffy.

@SteveJessop If they made the runway, then there wouldn't really be any reason for the landing not to be successful. Airliners can land just fine without power (just like almost every other type of airplane.)

This is an excellent answer, but I'd like to add one point. Before the Hudson case, ditching was considered the least favorable option for a forced landing. So, as a pilot, I admire and respect the cold and fast analysis of the situation and the decision to land the plane in the river. I've flown a similar flight in the sim, and the aircraft handling part is easy, the decision making is not.

@Sami It's also notable that most pilots of light GA aircraft that I've spoken to still feel that ditching is the least favorable option in situations like this despite some good evidence to the contrary (a documented egress rate of over 90% if the aircraft went into the water under control). The airline folks have taken a valuable lesson from this incident, hopefully it sinks in for the rest of us too.

@voretaq7 I that a successful ditch attempt aims to avoid "sinking in"

I am not sure if you want to include this in your answer, but given the month of the year, part of the miracle was that there were no fatalities, and the aircraft ditched in winter in the Hudson ... hypothermia kills.  But I don't call it a miracle, personally, I call it a professional crew (cockpit and cabin) and some professionals who were first-responders, and people on boats, etc.

It's important to note that there were many elements of both skill and luck involved in the US Airways 1549 "miracle" landing - the NTSB report and NTSB deliberations make for an interesting day of study.
We can divide your question into two different segments:

1 - Could another crew have executed this ditching after losing both engines?
The answer here is "Probably" - transport-category aircraft are designed for ditchings, and crews receive some training on ditching procedures (though as the NTSB noted it's not a normal component of simulator training). In many ways a ditching is just a special subset of engine failure training in which your landing will be on water rather than dry land, so pilots are in part training for this eventuality from the beginning of their flight training.
The decision to ditch on the river is a judgment call - Sully chose it rather than trying to make a runway at nearby airports that he wasn't sure he could reach without crashing into a populated area.
If another captain were presented with the same situation they may elect to make the same decision. Speaking as someone who occasionally flies over that same river in a much smaller aircraft and at a much lower altitude it's a reasonable choice to make.

2 - Would another ditching in a different aircraft have similar results?
This is where luck starts to enter into the equation, and the incident starts to earn its "Miracle" label.
US Airways 1549 was operating on an aircraft equipped for extended over-water flight, even though that was not required for this particular flight. This means there were life vests onboard, as well as slide-rafts designed to be used in the event of a ditching in open water.
It's debatable how much this survival equipment contributed to the successful outcome: The NTSB found that many passengers didn't take their flotation devices, and because of airframe damage during the ditching some of the slide rafts were not accessible or usable during the evacuation, but the equipment was considered a positive element in survival factors for this incident.
The weather was also fairly favorable (while temperatures were below freezing it was a fair-weather day: No rain or high winds), and the location of the ditching placed the aircraft close to ferries and other vessels able to quickly effect a rescue of the passengers and crew, so they did not spend much time in the weather or water.  (This was noted in the NTSB deliberations: Technically the aircraft could have travelled further down-river, but doing so would have put it out by the Verrazano Narrows bridge, further from potential rescue vessels).

A related part of the "miracle" that you hint at: they landed close to ferries and rescue boats, preventing many cases of severe hypothermia, yet didn't hit anyone on the busy river.

"Ask the Pilot" author Patrick Smith addressed this question.  I'll include excerpts of his post here:

As the public has come to understand it, Sully saved the lives of
  everybody on board through nerves of steel and superhuman flying
  skills. The truth isn’t quite so romantic...
[The] nuts and bolts of gliding into water aren’t especially
  difficult. The common sense of water landings is one of the reasons
  pilots don’t even train for them in simulators...  and nowhere in the
  public discussion has the role of luck been adequately acknowledged.
  Specifically, the time and place where things went wrong. As it
  happened, it was daylight and the weather was reasonably good; there
  off Sullenberger’s left side was a 12-mile runway of smoothly flowing
  river, within swimming distance of the country’s largest city and its
  flotilla of rescue craft. Had the bird-strike occurred over a
  different part of the city, at a lower altitude (beyond gliding
  distance to the Hudson), or under more inclement weather conditions,
  the result was going to be an all-out catastrophe, and no amount of
  talent or skill was going to matter...
Nothing they did was easy, and a successful outcome was by no means
  guaranteed. But they did what they had to do, what they were trained
  to do, and what, presumably, any other crew would have done in that
  same situation. And let’s not forget the flight attendants, whose
  actions were no less commendable. Thus the passengers owe their
  survival not to miracles or heroics, but to less glamorous forces.
  They are, in descending order (pardon the pun): luck, professionalism,
  skill, and technology.
There’s little harm in celebrating the unlikely survival of 155
  people, but terms like “hero” and “miracle” shouldn’t be thrown around
  lightly. A miracle describes an outcome that cannot be rationally
  explained. Everything that happened on the river that day can be
  rationally explained.

It is impossible to answer your precise question with any authority, it would be pure speculation. What we can answer is what would happen if you took some non-randomly chosen crews and put them in a simulation of the events which occurred to Flight 1549.
The problem with this, is that every single one of those pilots knows what to expect, they know that they are about to get a simulated bird strike which will cripple both engines. They can plan in advance what course of action to take, and execute it immediately. Sully did not have this luxury, and there was a lag between the event and taking action.

Documents indicate nearly two dozen emergency simulations were flown by experienced aviators, including an Airbus test pilot, at the manufacturer's headquarters in Toulouse, France. Four out of four attempts to return to the closest La Guardia runway were successful, according to the safety board's summary. There were nine additional simulated attempts to land at La Guardia, either at different runways or under a scenario in which the plane was more severely disabled. Of those, three were successful.
But only those pilots who immediately decided to turn back toward La Guardia after the simulated engine problems made it. The board's document concludes that such a scenario fails to "reflect or account for real-world considerations such as the time delay" in recognizing the bird strike and to "decide on a course of action."

Source WSJ - Miracle on the hudson
If you are interested in more regarding the findings of the NTSB the report is public.

As the data cited in aeroalias' answer shows, answers to this question need not be pure speculation; some data is available to give an indication of what we might expect

@JonathanWalters the "precise question" I referred to started If a random commercial airline crew were placed in the same situation.... there was nothing random about the crews selected for simulations. Hence it would be speculation how a random crew would fare.

Wikipedia used to maintain a list of commercial airlines ditchings on water, but I cannot find it. I did find related accidents on the US Airways 1549 article though:
1963 Aeroflot Tupolev ditching on Neva River: Probably the most similar thing because it was total engine failure (starvation) and it ditched on a cold river, narrowly missing a bridge. All 52 people aboard survived. This was in 1963 in the Soviet Union.
Japan Airlines Flight 2: In 1968, this flight accidentally landed on water short of the runway. All 107 people aboard survived.
Pan Am Flight 6: In 1956, this flight experienced engine trouble and eventually ditched in the Pacific Ocean. All 31 people aboard survived. (Thanks to @CodyP for pointing this one out.)
I swear there was 1 more, in 1940 or 1943 or around there. Some commercial prop plane ditched in the Pacific Ocean and everyone survived. Cannot find the article, though.
(EDIT: I believe I found it. Honolulu Clipper. It was actually a military flight in 1945 transporting some troops. 2 out of 4 engines failed and it ditched on the Pacific, but everyone (37 people) survived and was rescued later. What makes it especially impressive is that the ditching happened around midnight local time.)
EDIT: finally did find the list here. It lists successful and unsuccessful ditchings on water by commercial aircraft.

What's needed is to compare the successful list with a list of ditchings on water where some or everyone died. Off the top of my head, I can only think of 1 right now: That flight that was hijacked over the Indian Ocean, starved of fuel, and ditched. I think about 100 died and 50 survived, but interestingly, I remember the Air Crash Investigation episode claiming that most people survived the crash only to inflate their life vests early and thus trap themselves in the fuselage.
There are plenty more crashes over the ocean, such as that Swiss Air flight that had a fire aboard, but they shouldn't count unless the pilots maintained controlled flight and attempted to ditch. Total loss of control due to fire or explosions should not count.
So to sum up, we can compare lists, though they are not very big. Weather and sea conditions at the time of ditch should be taken into account too.
And I also swear I remember this, maybe someone can confirm. Sully got awards saying things like "unique air achievement" but tried to explain it was not unique. I could have sworn he mentioned the successful Aeroflot Tupolev ditching on the river Neva on the Tonight Show with Jay Leno, but it was glossed over.
Luck undoubtedly plays a role when encountering water. Hydrodynamic forces are undoubtedly chaotic where a tiny variance can produce cascading feedback, or lack thereof. I think your question is in the right spirits because you mentioned both luck and pilot skill playing a role. Sully had a lot of glider experience, for example.

Don't forget about Pan Am Flight 6, that had several engine failures and was forced to land on the ocean. The only fatalities were fourty-four cases of live canaries.

I remember an Asian flight ditching in shallow river and the tail breaking off killing at least one flight attendant

The second-to-last paragraph should be And I also swear I remember this, **maybe someone can confirm.** Sully got awards saying things like "unique air achievement" but tried to explain it was not unique. I could have sworn he mentioned the successful Aeroflot Tupolev ditching on the river Neva on the Tonight Show with Jay Leno, but it was glossed over. but I don't have the reputation to make such small edits now that the site has graduated. (Fixes rememebr and Tuploev.)

@MichaelKjörling Thanks, made those edits.

Regarding the Ethiopian Airlines flight 961, the video clearly shows that it was not exactly controlled landing either. The hijackers were interfering with control, apparently not believing the pilot that they are running out of fuel. So even that does not really count.

From your list, the cases of Garuda Indonesia 421 (one death out of 60 aboard) and Laoag 585 (19 deaths out of 29) are the recent cases that are probably the closest to AA 1549 — both involved losing engines at a relatively low altitude (on approach and shortly after takeoff, respectively.)

@JanHudec I thought it was because all engines were out, so the pilots were flying on limited RAT power. Unless I missed something, the hijackers were not physically interfering with the final descent.  The Ram Air Turbine would provide much less hydraulic pressure than normal, making control difficult. AFAIK the same limited power was available on US Air 1549.

@DrZ214, heavier controls won't make the plane suddenly bank 10°. And the WP page clearly says “While still fighting with the hijackers, he tried to ditch the aircraft…”. So while I am not sure how precisely the events of the last few seconds are known, it is most likely the bank was due to interference from the hijacker(s).

Ditching in water after engine failure is a standard emergency drill for pilots.  It's not required, but I'd expect major airlines to train their senior pilots for this.  Over mainland US, it's unlikely to ever be relevant - it's having to ditch in the centre of a major city which makes this particularly exceptional.  However it's the only possible answer for an airliner flying over the sea.
A quick Google suggests that most recent water landings have involved substantial loss of life.  However it's probably fair to say that none of the airlines involved have a high reputation.  For higher-quality airlines, not only will the pilots be better trained, but the planes will be kept in better condition so the situation is less likely to arise.
For a comparable example though, the Gimli Glider was very much a one-off.  Had the first officer not served at Gimli, he almost certainly wouldn't have considered it at as a landing location.  And had the captain not been an experienced glider pilot, the aircraft almost certainly would not have reached Gimli or any other suitable landing location, and the landing would not have been survivable.  Whereas the Hudson incident was generally reproducable on simulators by skilled pilots, attempts to run the Gimli Glider incident on simulators only resulted in crashes by other pilots.

Actually, ditching is not part of most simulator scenarios.

According to the accident report (page 60), pilots were given a Powerpoint presentation about ditching at some point. There was no simulator training for it.

Another example where variables matter is Air Transat flight 236, which glided 120km after a fuel leak caused dual engine shutdown over the North Atlantic during a transatlantic flight - it successfully landed in the Azores. The variable being that the flight was abnormally routed much farther south on its track, if it had been on a normal track it would never have made the Azores or any other airfield.

There are no "miracles" in aviation, or anywhere else on this planet, for that matter. What Sully did was something all pilots are trained to do, ditch an aircraft in water if you have nowhere else to land.
The reason why Sully is celebrated is because he executed the ditching procedure flawlessly and in so doing, ensured the safety of his entire crew and all pax. Part of it was luck, the vast majority was skill. Remember as well that there are aircraft that are designed to operate exclusively off water -- they are called "seaplanes."
My beef with the movie is that it is extremely disrespectful to the NTSB investigators and from that point of view, historically inaccurate in a gratuitous manner. Tom Hanks should be ashamed of that.

he executed the ditching procedure flawlessly This statement is factually incorrect: Sully's landing was far from perfect (a number of issues were called out in the NTSB report - key among them are excessive sink rate & angle when contacting the water and failure to fully complete the ditching checklist). Ultimately this didn't have a material impact on the outcome, which was without question almost the best we could ask for in such a situation, but "flawless" is a vast overstatement.

The question defines miracle as "But was it really exceptional?" and it should be noted that the word "miracle" comes from popular usage of the phrase used to denote this particular incident.  As such, the first and third paragraphs are, at best, comments, and the middle paragraph isn't differentiable from other answers already given. Please consider adding more detail to the meat of your answer, and removing, or at least de emphasizing, portions irrelevant to the question.

Given the limitations imposed by the situation, I will stick to my description of "flawless" as defined by the outcome, and not an inconsequential focus on the details of the process of how that outcome was achieved. And frankly, criticizing sink rate and angle when both engines were out is pathetically absurd.

@JuanJimenez The criteria for "flawless" is not an outcome-based one, it is a consideration of all the performance factors leading up to that outcome, as well as the outcome itself (and whether the criteria for perfection are achievable in specific circumstances). As an example a pilot can have a beautiful "greaser" landing after a lousy approach - that outcome doesn't make their performance "flawless", nor does it guarantee a similar outcome for the next pilot who makes similar errors.

@JuanJimenez  I agree with voretaq7.  A Formula 1 driver winning a race does not mean his driving was flawless, nor does breaking a world record mean the athletic performance was flawless.  Flawless means "without any mistakes or shortcomings" in the Oxford dictionary, not "successful" or "reached all the desired objectives."  Perhaps you could replace "flawlessly" with "exemplary" or "successfully"

@voretaq7 and CodyP There will always be people who think they can Monday-morning-quarterback everything that happens when 1) they were not there and 2) they will never have to do the same. I stand by my assessment of his actions as flawless on the basis of the outcome. A thousand things could have gone wrong that day and resulted in everyone on the aircraft and possibly innocent bystanders losing their lives. Sully made a flawless recovery and ditching execution, and everyone walked away. Just accept it and move on.

@JuanJimenez Perhaps the word you are looking for is "successful". At the end of the day, it was the distinction between a successful and unsuccesful ditching that saved lives, not whether the ditching satisfied someone's criteria of "flawless".

"Tom Hanks should be ashamed of that" is  unfair, since the director was Clint Eastwood.  I agree that the depiction of the  NTSB was negative for (IMO) no compelling narrative reason.  What was obvious was that they took the place of all second guessers and pundits (to include a site like this) who Monday Morning Quarterbacked the events of Flight 1549.

Tom Hanks should have known better than to accept the role under those circumstances. He's a big enough name that he can demand that the script be changed if necessary. Happens all the time.


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What is the crank on the ceiling of this aircraft?
What is the crank the pilot is operating above his head? Also what type of aircraft is this?

 image source

Where did you get the image from? Is this a frame grab out of a video? Mind attributing the source?

I'm pretty sure that's out of Friendly Skies Film's YouTube channel, though exactly which video I don't know...

This is not the video from which this picture came, but it explains which way to turn the crank.

Aha, I was right! It was from his channel. That scene starts here. The plane is N8831N.

Oops, added the citation. It's a screen grab from the linked YouTube video

It's an engineless helicopter. That's the crank that turns the main rotor. :)

The pilot is operating the overhead stabilator trim crank in an early model Piper Cherokee. Here's a close up the trim crank:

Piper Cherokee overhead trim crank; image from tnwings.com
In later models, it was replaced with airliner type trim wheels

I commented on the other answer but the Comanche's also had this, it isn't clear which of the piper PA-24, 28 just from the picture. It may even be a Twin Comanche

@RonBeyer In other places in the video I grabbed that from they show a PA-28-151, reg # N8027F. Most likely the same plane. Hadn't thought of checking the tail num when I posted the question :) Never seen a trim crank on the ceiling before. But, I've never been in a piper before either

@TomMcW As I previously mentioned to you, the plane in your screenshot is N8831N. (See this video for the explanation.)

That's a pitch trim control.  The older PA-28-140 Warriors had their manual elevator (stabilator) trim as an overhead crank like that.  Later versions of the PA-28 moved the trim to a friction wheel between the front seats behind the flap lever.

The Comanche's have it too, I occasionally fly a PA-24-180 with the ceiling trim crank. A good way to remember how it works is you screw it in to go up, and unscrew it to go down.

@RonBeyer Better not screw it up!

My 1968 Cherokee has this design and when you first start to fly it you have to think about which way to crank. After a while you don’t think about it anymore and your hand just knows which way to crank.

@JScarry Yep, becomes totally automatic after just a few hours. The same issue presents on trim wheel type systems; you just learn it with time.


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What steps have been taken to rule out instrument failure due to blocked static ports or pitot tubes?
In the case of Aeroperu Flight 603, a fatal crash was caused by duct tape that was accidentally left over some or all of the static ports on the underside of the fuselage after the aircraft was cleaned. As the static ports are critical to the operation of virtually all of those flight instruments that provide aerodynamic data regarding airspeed, altitude and vertical speed to the pilots and to the aircraft's computers, this bit of duct-tape caused the total failure of multiple basic flight instruments.
Another crash was caused for a similar reason: pitot tubes that were blocked by an insect led to flight instrument failure, and later, a tragic crash. This was Birgenair Flight 301.
These accidents happened in the mid-1990s. Today, two decades on, are there better systems in place to ensure that static ports or pitot tubes don't get blocked, causing instrument failure?
Edit 1: In both these flights, the pre takeoff checks missed out on the blocked static ports/pitot tubes. Human error clearly happened at this stage. Question is, have an steps been taken to make the flight instruments proof to this particular human error?

I'm not a pilot, but shouldn't a pre-flight inspection of the plane show random bits of duct tape sticking to the fuselage where they shouldn't be? If that's the case, no amount of technology will fix stupid pilots.

@Freeman Although the tape should have been detected during pre-flight checks the static ports are several feet in the air and the flight took place in the middle of the night. I'm not sure how the aircraft was painted but if the part where the static ports are is grey the duct tape would be tough to see.

@TomMcW  Thus the requirement (now) that the tape used for covering the static ports is bright & contrasts with the surrounding paint so it is easy to see. And at night, any walkaround should be performed with a flashlight, so that the pilot can see them (as well as plenty of other things).

@Ralph j I used to watch the pilots doing their walk-around with flashlights and wonder how they could possibly be certain they didn't miss anything. Seems like they'd only catch stuff if it was pretty obvious. Something like the wasp nest in the Birgenair crash would require going up on a lift to see it.

The best thing way to mitigate an issue like this is to draw attention to during the preflight check. Its becoming common to use covers that have a nice big red "Remove Before Flight" tag on them. These should be used as much as is practically possible (storage, cleaning, maintenance etc.)
Something like this would do nicely.

(source)
Similarly the aircrafts paint may be done in such a way to make the port stand out.

(source)
Caps/Covers for both static ports and Pitot Tubes are generally a good idea and can help prevent a clog that occurs while the plane is on the ground. As with anything diligence during preflight is key to avoiding this issue.
Most larger aircraft pilots call out "airspeed alive" during their takeoff roll as a way of confirming the Pitot system is working. If the air speed indicator does not read, the general procedure is to abort the takeoff.
Some aircraft may also be equipped with a radar altimeter which can help mitigate serious issues by providing an altitude system not based on the static system. However this only works at lower altitudes.

A clogged static port is a little bit more difficult to recognize on takeoff than a pitot port being cligged.
If the pitot was clogged, during takeoff there would be either no indication of airspeed or an extremely low value.  The pilot monitoring should recognize this during takeoff and call for an abort.
If all the static ports are clogged, the pilots would only recognize it after takeoff.  Without accurate altitude info, it would be difficult to land safely in IMC conditions.  The transponder altitude and altitude input to a non-WAAS GPS would inaccurate.
In all the airplanes I fly, each Air Data Computer has a static port on each side of the airframe to preclude a simple piece of tape of causing disaster.  Not only that, there is usually another static port that is just for the standby instruments, airspeed and altimeter.  Making something that happened before less likely.
As @Freeman states, a thorough preflight should catch those issues.

Unfortunately with the static port issue if there is tape over one port there's probably tape over all of them. Redundancy would be negated. Is there no way to test that the instruments are getting good data before take off?

Not necessarily.  The mechanic or washer could have started getting the tape off, got distracted and didn't get the tape from the other ports.

Certainly true. What I'm saying is that redundancy is a great way of accounting for most types of failures and, like you say, that makes the problem much less likely. But there are situations, like on the Aeroperu accident, where all the ports can be blocked. That being the only accident I know of where happened indicates that it is almost always caught in preflight but you say if they are all blocked there'd be no way to know until you were airborne, at which point you'd be in a real pickle without visual refs. Seems like that particular accident is still a possibility unless there's some oth

... cont way of verifying the static data.

Known pitch & power settings, GPS groundspeed, radio altitude, ILS glidepath... It can't be fun, but you don't lose EVERYTHING with complete pitot-static failure.

If all of the static ports were covered by something stiff enough (duct tape might be too flexible), I would expect you would notice just after take off that your altitude isn't increasing. I think it would be more difficult if some are working, as you would have to determine which one is invalid.


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Would a headwind result in a faster propeller rpm?
A few weeks ago I did an experiment with a model aircraft that has a motorized propeller. I turned on the propeller and it turned at a constant speed. Then I turned on a desk fan and put it in front of the propeller (see the picture below) and I saw an increase in propeller rpm and an increase in noise.
Does this also happen to a propeller when a headwind hits it?

You need to clarify this a lot.  active propeller - what is this?  I turned on the propeller - so it's driven by a motor? propeller remained at a constant speed - how did you measure it?   30% increase in thrust - how do you know?  How did you measure it?  If the aircraft was spinning in a circle, how could the fan generate a crosswind?  The ultimate answer is that all a crosswind does is to change the vector of the relative airflow hitting the propellor blades.

@Simon its an estimate.it was also on the floor it had no strings attached to it. Wasn't spinning in a circle. I will upload a picture soom

How was the thrust vector of the propeller oriented relative to the wind from the fan?

@Simon Made some edits so you can understand what I mean.

@mins Made some edits hope you can understand it now.

Did you put the fan beside the propeller to simulate a crosswind?

The edit definitely helps to clear things up. But it's still not clear how you are measuring thrust.

What you have pictured is a headwind, not a crosswind. A crosswind would be if you're blowing the aircraft from the side. Which are you wondering about?

Is the propellor free wheeling?

By faster, I suppose you mean you saw the propeller rotating faster. Feel free to reverse my edit if that's not what you meant.

@kevin it spun faster and it was louder. Great edits.

Are you sure the increase in noise came from the propeller, not from turning on the fan? Unless you have a pretty ( extremely ) sophisticated audio set up, you'd be pretty hard pressed to tell the difference.

The problem is you're holding the aircraft with your hand.
Imagine a windmill. It has no power at all, it spins freely. What happens when wind is blowing at it? It turns.
Now imagine a propeller with no power connected to it, so it acts like a windmill. If wind is blowing at it, it will turn just the same. Why? Because a propeller pushes wind backward when it turns. When it is facing a headwind, the propeller wants to turn such that it is pushing air at the same speed as the arriving air.
In your case, I suppose the fan is blowing air at a faster speed, compared to the propeller is pushing air on its motor. Say the motor pushes air backward at 1 m/s. The fan blows air at 2 m/s. That's why it spins faster with the fan on.

But that's only true as long as you're holding the aircraft with your hand.
In flight, nothing is holding the aircraft at a constant ground speed. For example, assume in a no wind condition, an aircraft is flying at 80 knots. Suddenly it encounters a 10 knots headwind, and continues to fly into this headwind for the remainder of the flight. What happens?
At the moment of encountering the headwind, the airspeed indicator in the cockpit jumps from 80 to 90. The propeller rpm will also suddenly jump to a higher value. But that is not going to last. The aircraft is getting pushed backward by the wind, the airspeed is going to slowly drop back to 80. There is not enough power to keep the propeller at the higher rpm which pushes air at 90, it can only to 80. After a while, it is flying at 80 knots relative to the air, and 70 knots relative to the ground.

would you care to comment on another situation - do you think a 3-blade prop would outperform a 2-blade prop in windshear situations? For example, if you were to fly missions ~3k AGL over peaks of mountains would you prefer a 3-blade prop, assuming the engine power is sufficient (260hp Lycoming mounted on RV-10). The question of 3 vs 2 blades often appears on various forums and majority of answers focus on top-speed where a 2-blade is marginally better, but I'm not concerned with the top-speed.

A propeller is always facing a headwind, it's called "airspeed". I don't really know what to tell you, the wind relative to the ground doesn't matter to the airplane or the propeller, the wind hitting it head on does, and yes, as the airspeed increases the load on the prop is reduced and the RPM increases unless you have a constant speed propeller (and thus a governor that changes the pitch of the blade when the RPM increases to combat this).
A wind shear does indeed change the airspeed momentarily (more so for larger aircraft with more momentum), but so does pitching over and diving.
The net effect is that a "headwind" (as measured relative to the earth) will only affect your ground speed, and thus the time it takes to get to your destination. The headwind, as measured relative to the aircraft, is called airspeed, and is usually kept at some set value appropriate for the aircraft in cruise. If the airspeed increases abruptly, the RPM will increase slightly as the load decreases (air doesn't have to be accelerated as much), which is countered by the prop governor (if you have one) and the fact that the airplane will slow down to match the new headwind since you're not feeding it any more power to maintain the new higher airspeed.

Surprisingly, the answer is yes for geared engines.
With geared engines, the propeller has enough mechanical advantage to drive the gearbox (rather than the engine driving the gearbox). This can hurt the gearbox and the engine.
The Rotax engine employs a built-in 2.4:1 reduction gearbox. When descending, you are not supposed to reduce power, otherwise the propeller will push on the gearbox and the engine (rather than the engine turning the gearbox and then the prop).

authors: محمد جواد کریمی


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Which part of aircraft is contributing the most weight of airplane?
Which part of the aircraft contributes the highest portion of weight?
Note: we had argument that, wires connecting the avionics systems are the major contributors of aircraft weight. Due to some issues with optical fibre technology this is not been used in aviation yet. So my question arises as mentioned above.

A380-800: Total wire count: ~100 000, Total wire length: 470 km, Total weight of wires: 5,700 kg.

@mins 5,700 kg is huge weight for the aircraft, I'm sure there are many technologies are popping up in the field to make it wire free?

@mins, I think this also includes all the electrical wiring (i.e. to provide power to lighting etc.). They say that 30% of this wiring is a candidate for wireless, so I think 30% of these cables is used to transfer data (and relevant for an optical fibre discussion)

@lucky, 5700 kg is only 1% of the max takeoff weight of the A380.

@Lucky: If you read the linked document,it's about scrubbing weight using wireless ("About 30% of electrical wires are potential
candidates for a wireless substitute!"). For data wires, using bus, serial, networking and multiplexing are also common solutions (that is already partially used today). However this comes with additional complexity and security concerns.

It would be very strange if that part is the same both for Mrija and for paraglider.

Fuel: It weight from ~20% for short-haul medium airliners (b737NG) to ~38% for long-haul jumbo(A380) in terms of Maximum takeoff weight

Aerospace Engineering e-Mega Reference shows the following table for two aircraft (the large commercial jet, the B747-100, and the military jet, the C-5A). You can see that it differs quite a lot between the B747 and the C-5 already, so it's hard to give a definitive answer for all aircraft in general.
Also, it depends a lot on how you break down the components, for example, here the Nacelle and Propulsion system are shown separately, but if you combine the two (and some others as is done in the dry engine weight, I think) things could change.
The Aerospace Engineering e-Mega Reference points to Beltramo as the source for the numbers. Perhaps you could find some information there about what belongs to which group.
However for both aircraft, it can be seen that the Wing and the Airframe are significant contributors (and for the B747 furnishing is also a large part of the weight)
I think they included all the wiring in the Avionics part (that would make sense to me), but still it is a relatively small part of the total weight.

I wonder what the distinction between "propulsion system" and "dry engine weight" is ...

That's always the difficulty with these tables. I think the dry engine weight would also include the nacelle weight (and perhaps the pylon weight?).

@HenningMakholm: The propulsion system includes all stuff like the engine quadrant in the cockpit, the propellers (if any are fitted) and (now the definition becomes softer) everything forward of the firewall / all engine mounts, cooling and lubrication liquids. The dry engine is just the engine as it comes from the manufacturer, not even with oil inside.

I checked the original source (link in my answer) and it states:
"The propulsion system includes the engines (which are not considered in this study), the fan exhaust thrust reverser system, the engine exhaust thrust reverser/spoiler system, the engine system and fuel system. The fan exhaust thrust reverser system includes the translating structure, cascades, blocker doors, fan exhaust ducting located with the translating structure, and the actuation system and controls. ...

... The engine exhaust thrust reverser/spoiler system includes all of the structure and systems located aft of the engine turbine exhaust flange which include the thrust reverser, tailpipe and bullet. The engine systems include components for cooling, lubrication, ignition, throttle, and starting as well as the water injection system and cockpit controls. The fuel system includes the fuel fill and drain system, fuel distribution system, fuel vent plumbing, fuel dump system, integral wing tank sealant, and supplemental fuel tanks."

So in short, the propulsion system is everything related to the engine but the engine itself and the nacelle.

Electrical system is called out separately from Avionics, so I would think wiring would be in Electrical system. But, it's hard to tell for sure from just the chart.

If you mean by part of aircraft it will be the landing gear.
But if you mean what other stuff add weight you have the electronic entertainment system that adds alot of wires and cables which add weight to the airplane but with no operational use for the airline its only to entertain passengers.


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Am I required to obtain a student license before a sport, recreational, or private one?
I want to double check if my first step in obtaining a sport, recreational, or private license is to obtain a student license.  I'm assuming student license always comes first, but want to make sure.  :-)
I want to make sure that isn't a less expensive way to go than this -- jumping into a more intensive program to go "straight" to the higher level licenses.  Want to make sure getting a student license first doesn't financially waste some of the classes, training, or flight hours you pay for -- by them not counting toward the higher level licenses -- where if you had done it differently you would have saved money.
I'm not talking about less learning, just how it's done.  (Making sure high enough licensed instructors, right classes, etc.)
As an addition... Do you jump through student, sport, recreational, to private?  Or, do you go from student which whichever of these you want?

What country are you in?

Hi. When asking about licensing, regulation etc, please always state the jurisdiction you are asking about.

Sorry, United States (Michigan.)

A student pilot certificate is just a medical certificate printed on yellow paper instead of white paper and with endorsement templates for soloing printed on the back.  Other than that presentation difference it is no different than the medical exam a certificated pilot takes for whatever class medical you apply for.  The fee for this varies by examiner and may set you back $75 or so, but that (and being able to pass a medical) is the only barrier to entry.  There is no flight training or knowledge requirement to get this certificate.
Once you have a student pilot certificate / medical you have one of the requirements to solo and can train directly for any of the sport, recreational or private pilot certificates.  You'll want to focus on sport or private training, as pretty much no one pursues recreational certificates.

If you do go for sport initially with plans to later upgrade to private make sure you use a full CFI, not a CFIS so you can carry the hours forward.

Yes. In order to get other type of licenses, you need to have a student pilot license.
After getting a student pilot license, you can apply for a sport, recreational or a private license. For a commercial pilot license, you need a private pilot license (or should be a military or former military pilot with some conditions).
These eligibility requirements can be found in Code of Federal Regulations Title 14 ID Part 61.